1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to a method and apparatus for transmitting a Short Message Service (SMS) message in a wireless communication system supporting an idle mode Mobile Station (MS).
2. Description of the Related Art
In the 4th Generation (4G) communication system, which is the next generation communication system, research and commercialization are being conducted to provide users with various services having a data rate of about 100 Mbps or more. In particular, research on the 4 G communication system is now being conducted to support high-speed services in the way of guaranteeing mobility and Quality-of-Service (QoS) for a Broadband Wireless Access (BWA) communication system such as wireless Local Area Network (LAN) system and wireless Metropolitan Area Network (MAN) system. One example of a 4 G communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.
According to the IEEE 802.16 communication system standard, in a case where traffic to be transmitted/received does not exist during a predefined time, a Mobile Station (MS) operates in an idle mode and minimizes power consumption. The MS wakes up from the idle mode during a paging listening interval and receives a paging message. The paging message includes information instructing the idle mode MS to perform a network reentry operation such that the idle mode MS transitions from the idle mode to a connection mode (i.e., a connected state) because there exists DownLink (DL) data to be forwarded to the idle mode MS, instructing the idle mode MS to perform location update, or the like. The DL data includes SMS information to be transmitted to the idle mode MS. In a case where an SMS message of the idle mode MS is on standby, a Base Station (BS) has to instruct the idle mode MS to perform the network reentry operation using the paging message.
On the other hand, the IEEE 802.16m communication system provides a method in which, in a case where there is a need to transmit an SMS message to an idle mode MS, the idle mode MS can receive the SMS message without a transition process from the idle mode to a connection mode (i.e., a connected state). A process of supporting SMS message transmission to the idle mode MS defined in the IEEE 802.16m communication system is described below with reference to FIG. 1.
FIG. 1 is a ladder diagram illustrating SMS message transmission from a BS to an idle mode MS in a wireless communication system according to the related art.
Referring to FIG. 1, while the MS 100 performs a paging non-listening interval operation of an idle mode in step 101, the BS 150 receives an SMS message for the MS 100 in step 103. In step 105, the MS 100 performs a paging listening interval operation. In step 107, the BS 150 transmits a paging message including information for the MS 100, to the MS 100. The paging message of step 107 includes information instructing the MS 100 to perform a location update process. Upon receiving the paging message including the information instructing the MS 100 to perform the location update process from the BS 150 in step 107, the MS 100 proceeds to step 109 and transmits a ranging code to the BS 150. In response to the ranging code transmitted in step 109, in step 111, the MS 100 receives a ranging code response message from the BS 150. In step 113, the MS 100 transmits a ranging request message, including an indicator informing that the MS 100 is performing a location update process, to the BS 150. After receiving the ranging request message of step 113 from the MS 100, in step 114, the BS 150 transmits a ranging response message including SMS information.
The transmission of the SMS message to the idle mode MS in the IEEE 802.16m communication system described above with reference to FIG. 1 utilizes the ranging message that is used in the ranging process. However, the combining of the ranging process with the SMS message adds complexity to the processing by the idle mode MS and thus, there is a need for a way of transmitting the SMS message to the idle mode MS irrespective of the ranging process.